Nitric oxide in tumor biology and cancer therapy. Part 2: Therapeutic implications

Signaling and physiological activity of the NO-donating agent TNICthio in human blood lymphocytes, Jurkat and MCF7 cell lines

Signaling and physiological activities of the crystalline tetranitrosyl iron complex with thiosulfate-a NO-donor (TNICthio) were first studied on human cells in conditions of mono and combined application of H₂S and antioxidants. Comparative studies were performed on three cell lines: normal and leukemic T lymphocytes (Jurkat cells) and breast cancer MCF-7 cells (human breast adenocarcinoma). Also established was a high biological activity of TNICthio, as well as correlation between the levels of reactive oxygen species generation, the formation of double-strand breaks (DSB) in DNA and cell proliferation. The amount of DNA DSB repair in normal lymphocytes was tenfold higher than in leukemic cells. Inorganic H₂S donor sodium hydrosulfide (NaHS) had insignificant effects on the production of reactive oxygen species and generation of DNA DSB in the cells of all the lines under study. However, H₂S increased the tolerance of cells to the stress response after combined cell treatment with NO + H₂S. 0.5 mM NO-donor and 0.1 mM antitumor antibiotic doxorubicin were equally effective generators of reactive oxygen species in MCF-7 cells; however, antiproliferative activity of the NO-donor, in this case, proved to be twice higher. The results obtained in this work may be promising for the prediction of pro- and antioxidant properties of the new NO and H₂S donating compounds, as well as for the development of methods for complex anticancer therapy.

Subcellular Energetics and Metabolism: A Cross-Species Framework

Although it is generally believed that oxidative phosphorylation and adequate oxygenation are essential for life, human development occurs in a profoundly hypoxic environment and "normal" levels of oxygen during embryogenesis are even harmful. The ability of embryos not only to survive but also to thrive in such an environment is made possible by adaptations related to metabolic pathways. Similarly, cancerous cells are able not only to survive but also to grow and spread in environments that would typically be fatal for healthy adult cells. Many biological states, both normal and pathological, share underlying similarities related to metabolism, the electron transport chain, and reactive species. The purpose of Part I of this review is to review the similarities among embryogenesis, mammalian adaptions to hypoxia (primarily driven by hypoxia-inducible factor-1), ischemia-reperfusion injury (and its relationship with reactive oxygen species), hibernation, diving animals, cancer, and sepsis, with a particular focus on the common characteristics that allow cells and organisms to survive in these states.

Nasal nitric oxide in relation to quality-of-life improvements after endoscopic sinus surgery

BACKGROUND

The level of nasal nitric oxide (nNO) in patients with chronic rhinosinusitis (CRS) has been proven to increase after surgical treatment. The relationship between nNO and treatment outcome has not been documented to date.

OBJECTIVE

To evaluate the levels of and changes in nNO after sinus surgery and its effects on quality-of-life improvements for patients with CRS after surgical treatment.

METHODS

By using a clinical cohort study design, we identified patients who were receiving bilateral endoscopic sinus surgery for CRS with nasal polyps (CRSwNP) and CRS without nasal polyps (CRSsNP) with a 1-year follow-up. We assessed the demographics, preoperative prognostic predictors, pre- and postoperative nNO levels, and disease-related quality of life via a questionnaire.

RESULTS

Sixty-nine patients were enrolled, including 53 with CRSwNP and 16 with CRSsNP. The CRSwNP group had lower initial nNO levels and higher endoscopic and image scores but similar demographics and questionnaire scores. In the patients with CRSwNP, nNO levels recovered and reached a plateau at the third month after surgery. However, nNO levels in the CRSsNP group continued to increase until 6 months after surgery before reaching a steady level. Higher preoperative nNO levels were significantly related to better quality-of-life improvements at 3 months after surgery in both groups.

CONCLUSION

The nNO levels in patients with CRS increased and reached a plateau after sinus surgery for both groups. Under similar subjective disease severity, the CRSsNP group had higher preoperative nNO levels and maintained a continuously longer rise before reaching a steady level after surgery. For both CRS groups, a higher initial nNO level brought better quality-of-life improvements and could be provided as a preoperative prognostic indicator.

Induced nitric oxide synthase as a major player in the oncogenic transformation of inflamed tissue

Nitric oxide (NO) is a free radical that is involved in the inflammatory process and carcinogenesis. There are four nitric oxide synthase enzymes involved in NO production: induced nitric oxide synthase (iNOS), endothelial NO synthase (eNOS), neural NO synthase (nNOS), and mitochondrial NOS. iNOS is an inducible and key enzyme in the inflamed tissue. Recent literatures indicate that NO as well as iNOS and eNOS can modulate cancer-related events including nitro-oxidative stress, apoptosis, cell cycle, angio-genesis, invasion, and metastasis. This chapter focuses on linking NO/iNOS/eNOS to inflammation and carcinogenesis from experimental evidence to potential targets on cancer prevention and treatment.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

Hypoxia and free radicals, such as reactive oxygen and nitrogen species, can alter the function and/or activity of the transcription factor hypoxia-inducible factor 1 (HIF1). Interplay between free radicals, hypoxia and HIF1 activity is complex and can influence the earliest stages of tumour development. The hypoxic environment of tumours is heterogeneous, both spatially and temporally, and can change in response to cytotoxic therapy. Free radicals created by hypoxia, hypoxia-reoxygenation cycling and immune cell infiltration after cytotoxic therapy strongly influence HIF1 activity. HIF1 can then promote endothelial and tumour cell survival. As discussed here, a constant theme emerges: inhibition of HIF1 activity will have therapeutic benefit.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

Preoperative plasma vascular endothelial growth factor but not nitrite is a useful complementary tumor marker in patients with colorectal cancer

PURPOSE

Vascular endothelial growth factor and nitric oxide are both related to tumor progression. This study was designed to measure preoperative plasma vascular endothelial growth factor and nitrite levels in patients with colorectal cancer to evaluate their clinical applications as tumor markers.

METHODS

In total, 279 patients with primary colorectal cancer and 20 patients with hemorrhoids (as a control) were included in this study. Plasma vascular endothelial growth factor was measured by quantitative, solid-phase, enzyme-linked immunosorbent assay (R&D Systems), whereas nitrite was measured by a high-performance liquid chromatographic method.

RESULTS

The vascular endothelial growth factor (mean, 220.6 pg/ml, P < 0.005) and nitrite (mean, 29.4 microM, P = 0.043) levels of patients with cancer were significantly higher than those of controls (mean vascular endothelial growth factor, 67 pg/ml; mean nitrite, 23 microM). Preoperative plasma vascular endothelial growth factor levels were positively correlated with tumor stage, T class, M class, and tumor size (Spearman correlation, P < 0.01), but were not associated with gender, N class, tumor location, histology type, or grade. There were no statistical differences in nitrite levels among different groups of patients with cancer. Higher vascular endothelial growth factor levels also were correlated with leukocytosis, elevated carcinoembryonic antigen, and a higher platelet count. The positive rates of vascular endothelial growth factor elevation (>148.6 pg/ml) compared with carcinoembryonic antigen elevation were 36.9 to 14.6 percent in Stage I, 60.9 to 33 percent in Stage II, 62.9 to 48.7 percent in Stage III, and 86 to 70.2 percent in Stage IV, respectively. The overall positive rate of vascular endothelial growth factor elevation also was higher than that of carcinoembryonic antigen elevation (63 percent for vascular endothelial growth factor vs. 42.5 percent for carcinoembryonic antigen, P = 0.016). More than one-half of the patients without carcinoembryonic antigen elevation still had elevated vascular endothelial growth factor levels. The combined assessment using vascular endothelial growth factor and carcinoembryonic antigen was superior to individual assessment using vascular endothelial growth factor or carcinoembryonic antigen. In node-negative tumor, the patients with vascular endothelial growth factor elevation had worse disease-free survival than those without vascular endothelial growth factor elevation (P = 0.0367). There was no association of vascular endothelial growth factor elevation with survival in patients with node-positive tumor.

CONCLUSIONS

Plasma vascular endothelial growth factor is a useful complementary tumor marker; however, synchronous measurement of white blood cells, platelets, and carcinoembryonic antigen is suggested in the clinical application of vascular endothelial growth factor to colorectal cancer.

Inducible nitric oxide synthase and bcl-2 expression in nasopharyngeal cancer: correlation with outcome of patients after radiotherapy

PURPOSE

The expression of inducible nitric oxide synthase (iNOS) and bcl-2 proteins was evaluated and the prognostic significance determined in nasopharyngeal cancer (NPC) patients treated by radiotherapy.

METHODS AND MATERIALS

Tissue sections from 55 patients with NPC were assessed for iNOS and bcl-2 protein expression by immunohistochemistry, immunoelectron microscopy, and in situ hybridization before treatment. The markers were correlated with apoptosis (detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay) and clinicopathologic parameters.

RESULTS

All NPC sections exhibited positive iNOS and bcl-2 immunoreactivity, with a mean percentage of 6.24% +/- 0.58% and 17.09% +/- 2.48%, respectively. A significant positive correlation was observed between iNOS expression and the apoptotic index (p < 0.0001, Pearson's r = 0.8518), and bcl-2 expression correlated inversely with apoptosis (p = 0.0001; Pearson's r = -0.6170). A significant inverse correlation was found between iNOS and bcl-2 immunoreactivity (p < 0.0001, Pearson's r = -0.7144). Bcl-2 but not iNOS expression was associated with the stage of the tumor according to the criteria of the American Joint Committee on Cancer (1997) (p < 0.0001). Patients who had recurrence of the tumor and metastasis after radiotherapy had a lower expression of iNOS (p = 0.014 and p = 0.035, respectively), although overall survival was not significantly different statistically. Higher bcl-2 expression was also associated with local tumor recurrence (p = 0.005) but not with metastasis or overall survival.

CONCLUSION

It appears that iNOS and bcl-2 expression may be potentially useful biomarkers for predicting the outcome of radiotherapy in NPC patients.

Genetic disruption of host interferon-gamma drastically enhances the metastasis of pancreatic adenocarcinoma through impaired expression of inducible nitric oxide synthase

Synergistic induction of the inducible nitric oxide synthase (NOS II) gene requires a combination of interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). In this study, we determined whether the induction of IFN-gamma was required for NOS II-mediated antitumor activity in vivo. Highly metastatic H7 murine pancreatic adenocarcinoma cells were implanted into the subcutis, footpad, and pancreas of syngeneic IFN-gamma(+/+) and IFN-gamma(-/-) mice. These cells grew and produced metastases and ascites in IFN-gamma(+/+) mice. In sharp contrast, the same tumor cells grew much more aggressively, metastasized more extensively, and produced a larger amount of malignant ascites in IFN-gamma(-/-) mice. Also, induction of IFN-gamma correlated with NOS II gene expression and NO production in IFN-gamma(+/+) injected with the tumor cells but not in IFN-gamma(-/-) mice or IFN-gamma(+/+) mice without tumor challenge. In vitro, only LPS plus IFN-gamma induced a high level of NO production and cytotoxicity against H7 cells. These data suggested that the tumor cells stimulated IFN-gamma secretion from host cells, which in turn stimulated NO production by host cells and suppressed tumor growth and metastasis.

Hypoxia modulated gene expression: angiogenesis, metastasis and therapeutic exploitation

Tumour hypoxia is the result of an imbalance in oxygen supply and demand. It is an adverse prognostic indicator in cancer as it modulates tumour progression and treatment. Many genes controlling tumour biology are oxygen regulated, and new ones are constantly added to the growing list of hypoxia-induced genes. Of specific importance are hypoxia-responsive transcription factors, as they can modulate the expression of numerous different genes. Similarly, growth factors which govern the formation of new blood vessels or which control blood flow are vitally important for both the maintenance of the primary tumour and metastases at distant sites. The purpose of this review is to present an update of selected issues regarding hypoxia-inducible gene expression and how this affects prognosis, angiogenesis and metastasis. It will conclude by discussing gene therapy as one possible means of exploiting tumour hypoxia for the treatment of cancer.

Nitric oxide production by tumour tissue: impact on the response to photodynamic therapy

The role of nitric oxide (NO) in the response to Photofrin-based photodynamic therapy (PDT) was investigated using mouse tumour models characterized by either relatively high or low endogenous NO production (RIF and SCCVII vs EMT6 and FsaR, respectively). The NO synthase inhibitors Nomega-nitro-L-arginine (L-NNA) or Nomega-nitro-L-arginine methyl ester (L-NAME), administered to mice immediately after PDT light treatment of subcutaneously growing tumours, markedly enhanced the cure rate of RIF and SCCVII models, but produced no obvious benefit with the EMT6 and FsaR models. Laser Doppler flowmetry measurement revealed that both L-NNA and L-NAME strongly inhibit blood flow in RIF and SCCVII tumours, but not in EMT6 and FsaR tumours. When injected intravenously immediately after PDT light treatment, L-NAME dramatically augmented the decrease in blood flow in SCCVII tumours induced by PDT. The pattern of blood flow alterations in tumours following PDT indicates that, even with curative doses, regular circulation may be restored in some vessels after episodes of partial or complete obstruction. Such conditions are conducive to the induction of ischaemia-reperfusion injury, which is instigated by the formation of superoxide radical. The administration of superoxide dismutase immediately after PDT resulted in a decrease in tumour cure rates, thus confirming the involvement of superoxide in the anti-tumour effect. The results of this study demonstrate that NO participates in the events associated with PDT-mediated tumour destruction, particularly in the vascular response that is of critical importance for the curative outcome of this therapy. The level of endogenous production of NO in tumours appears to be one of the determinants of sensitivity to PDT.

Immune-inflammatory mechanisms in IFNgamma-mediated anti-tumor activity

IFNgamma is a functionally pleiotropic cytokine which shows considerable potency in promoting anti-tumor functions in vivo. Despite limited efficacy when delivered systemically either to experimental animals or patients, IFNgamma appears to play an important and perhaps critical role in directing the development of immune-mediated tumor destruction when expressed within the tumor bed. This has been demonstrated both by use of tumor cells transduced to express IFNgamma and by the use of IL-12 which is able, at least is murine models, to promote an IFNgamma-dependent, T cell mediated anti-tumor response. Recent studies indicate that the therapeutic efficacy of IFNgamma in tumor models depends critically upon the ability of the tumor cells themselves to respond to IFNgamma. Though IFNgamma is able to induce anti-viral activity and has direct anti-proliferative effects on some tumor cell lines, immunomodulatory function also appears to be an important component of its anti-tumor action. This is mediated through the action of several different classes of IFNgamma-inducible gene expression which control antigen processing and presentation, leukocyte trafficking, and indirect tumor cytotoxicity.